This invention relates to nuclear reactor fuel elements.
The fuel elements of a nuclear reactor core may be arranged in discrete groups, each group being included in a replaceable construction termed a sub-assembly. One such sub-assembly which is used in a fast reactor cooled by liquid sodium comprises a hexagonal bundle of 127 slender fuel elements enclosed by a steel wrapper about the periphery of the bundle. The fuel elements are each helically wrapped with wire spacers which inhibit bowing and vibration and ensure efficient cooling. However, it is expected that in operation of the nuclear reactor the temperature of the fuel element sheath in the regions underneath the wire wraps will be higher than the remaining regions of the sheath due to the presence of stagnant coolant and to accommodate such a temperature differential the maximum operating temperature of the fuel element would be severely limited.